1. Field of the Invention
This invention relates to controlling a plurality of movable units and, in particular, to a plurality of storage shelf units positioned on a track for selective movement toward and away from one another using devices sensitive to heat, capacitance or reflected electromagnetic wave transmissions to initiate such movement.
2. Prior Art
Numerous systems have been disclosed for causing a plurality of units to move toward and away from one another along guided track arrangements wherein each unit is self-propelled. Manual switches mounted on the ranges are suggested to selectively move each unit in U.S. Pat. Nos. 3,829,189, 3,957,322, 4,017,131 and 4,039,040. Other systems use mechanical arrangements to determine range spacing (see, for example, U.S. Pat. No. 4,033,649). Some systems employ computer units to determine the movement of a set of electrically connected ranges (see, for example, U.S. Pat. No. 3,890,903).
Safety switches are proposed for most systems to stop the ranges to prevent personnel injury or damage to objects as shown in U.S. Pat. No. 3,865,446.
The present invention overcomes many inconveniences and complications of these earlier systems.